reCAPTCHA
PHP client library for reCAPTCHA, a free service
...The project bundles client and server examples, language-specific helpers, and documentation patterns for integrating reCAPTCHA v2 and v3 flows into web forms and APIs. Its design philosophy is “risk-based”: most users pass silently based on behavioral signals, while higher-risk interactions may be challenged with an image, checkbox, or other verification step. Site owners register keys, embed a small client script, and verify tokens on the server to protect actions like sign-ups, logins, and form submissions. The ecosystem supports mobile and enterprise variants, but the repo focuses on common web integrations and best practices for verifying the token securely. ...